There are several attributes of muscle tissue quality that relate to palatability and consumer eating satisfaction. Assessments of such qualities can be useful for a variety of food animals. Such assessments can also be useful in both live animals and animal carcasses. For example, one such important attribute is the amount of intramuscular fat (IMF) that exists in the longissimus dorsi muscle. Within the U.S., the longissimus dorsi muscle or “loin” is a very high value part of the pork carcass. IMF in the pork loin adds significantly to flavor and juiciness, traits that are highly related to eating satisfaction. The amount of the IMF in the pork loin is governed by genetics, age of the animal at time of harvest and to a lesser degree by other environmental factors and animal nutrition.
There is considerable variation in IMF from animal to animal or from carcass to carcass with mean values in the range of 2.0-2.5%. Carcasses with less than 2.0% IMF can be undesirable. Carcasses with more than 3.5% IMF are valued by high-end restaurant chefs that offer pork on their menus. Carcasses with more than 6% IMF are highly valued in some foreign markets, such as in Japan. Because of these market differences, the ability to noninvasively measure the amount of IMF in the pork loin has value to the pork packing plant as well as to other aspects of the muscle tissue-processing industry.
A significant challenge to measuring IMF in the packing plant is the speed by which carcasses are processed. As an example, with many plants running their chain speed at 1200 carcasses per hour, a carcass would be measured in less than 2 seconds if the carcass is going to be measured during the packing process. In addition, pork carcasses are not routinely split anywhere along the loin that would expose the internal tissue for either a subjective or quantitative measure of the amount of IMF in the lean tissue. Consequently, packing plants have sought efficient and practical methods of noninvasively “looking” inside the loin muscle and determining the percentage of IMF as compared to the amount of lean tissue.